Multirange receiver



Dec. 27, 1938. A, A, UNSELL- 2,141,756

MULTIRANGE RECEIVER Filed April 13, 1936 FREQUENCY CHA NGER sw/rm oseArm/a MEMBER 547 INVENTOR ALFEED A. L/N$ELL 'ATTORNEY Patented Dec.27, 1938 PATENT OFFICE MULTIRAN GE RECEIVER Alfred A. Linsell, Sydenham,London, England, assignor to Radio Corporation of America, a corporationof Delaware Application April 13, 1936, Serial No. 73,989 In GreatBritain April 26, 1935 3 Claims. (Cl. 250-20) This invention relates toradio receivers and more particularly to multi-range tunable receiversadapted to receive over difierent wave length ranges.

Broadcast receivers for sound and music signals are at present inwidespread use and it is common to construct such receivers to betunable over two wave length ranges corresponding respectively to theso-called medium wave broadcast range (at present'from about 250 to 550meters) and to the so-called long wave broadcast range (at present fromabout 900 to 1900 meters). It is expected, however, that there willshortly be established in Great Britain a public service of televisiontransmission upon short wavesprobably upon waves in the neighborhood of7 meters longand the object of the present invention is to provide animproved economical and easily operated receiver which can be employedfor broadcast reception over a plurality of wave length ranges of whichone includes a short Wave'range for television signals. The problem ofextending a radio receiver which has been constructed to receive soundsignals on the ordinary present broadcast waves so that it may receivealso television signals on short waves involves more than merely makingprovision for the reception of signals within the further short waverange, for it will be appreciated that the width of frequency spectrumoccupied by television signals is much more than that occupied by soundsignals. Sound signals can be (and by international agreement at thepresent time are) accommodated within a band of frequencies equal to thecarrier 15,000 cycles, but the modulation frequency range involved intelevision may easily extend up to 2 megacycle or more. 7

For the purpose of convenience in description, radio receiving apparatusadapted to receive carrier frequency energy modulated with sound ormusic signals, will be hereinafter referred to as sound broadcastreceiving apparatus.

According to the main feature of this invention a radio receiver capableof receiving over a plurality of wave length ranges of which one is ashort wave television range, comprises sound broadcast receivingapparatus preceded by a heterodyne arrangement adapted to transform '50received short Wave television modulated signals for broadening. themodulated carrier frequency channel or channels in the sound broadcastreceiving apparatus to the extent necessary to enable saidchannel orchannels to pass the relatively wide band occupied by television signalsand for fixing the tuning of the said broadcast J5 receiving apparatusat a predetermined value corresponding to said intermediate frequency.Thus, although a radio receiver in accordance with this invention may beleft, after sound broadcast reception, with the controls for the '10variably tunable carrier circuits of the sound broadcast receivingapparatus anywhere within the range of variation (e. g. anywhere between250-550 meters or 900-1900 meters depending upon the wave length uponwhich sound broad- 16 cast reception has been last effected) thearrangement is made such that when the receiver is changed over totelevision reception said circuits are tuned to a predeterminedfrequency chosen as the intermediate frequency for such 20 reception.

Where the reception of low definition television signals-i. e.television signals which do not occupy a Width of spectrum materiallydifferent from that occupied by a sound program- .25 is contemplated, itis not necessary to broaden the carrier frequency channel or channels inthe sound broadcast receiving apparatus for such apparatus will serve,unaltered, for low definition television. :30

The invention is illustrated in the accompanying drawing wherein Figure1 shows diagrammatically a portion of a receiving circuit em. bodyingthe invention, Figure 2 shows a form of indicating dial that may beused, and Figure 3 :35

separate local oscillator and'frequency changer valves may be provided.The tuning'controls for the local oscillator and the input circuit ofthe .50 frequency changer are preferably gang controlled from a commonhandle as indicated by the line 5. Beat frequency energy from thefrequency changer is applied (after further amplification, if desired)to the input circuit of the 55 sound broadcast receiving apparatus whichinput circuit thus serves as a beat frequency circuit for televisionreception on short waves. This input circuit may consist of a coil 6included in the grid cathode circuit of a valve I and arranged to beshunted (for sound reception on broadcast waves) by a tuning condenser Sadapted to tunesaid coil over the sound broadcast wave length range inquestion. The said tuning condenser is in series with switch contacts 9,it, which are opened when the receiver as a whole is to receive shortwave television signals, the switch 3 being, in these circumstances,moved into a position (the position shown) in which the tuning condenseris cut out of circuit and instead there is shunted across the coil 6 asmall fixed condenser H shuntedby a resistance I2. This combination l l,i2, is put in circuit for shor wave reception through contacts 53, ill.The small fixed condenser H is of such magnitude as to tune the coil 6to a predetermined fixed frequency corresponding to the beat frequencyfrom the frequency changer 3 and the resistance [2 is of such magnitudeas to make the coil 6 when thus tuned, suificiently flatly tuned to passthe range of television modulation. For sound a broadcast reception anordinary broadcast aerial M is coupled to the coil 6 and the switch s ismoved into that position (not shown) in which the said coil 6 is tunedby the variable condenser 8 and the combination ll, I2, is out ofcircuit.

In the receiver illustrated in Figure 1 the sound broadcast receivingapparatus is itself of the superheterodyne type and accordingly theoutput of the valve 1 is mixed with local oscillations from a secondlocal oscillator 4 and applied to the input circuit of another frequencychanger valve M. This input circuit is arranged in'similar manner to theinput circuit of valve 1 and includes a switch 5 having contacts 9',Ill, 13' which in one position causes said input circuit to be tunableby a variable condensert' over the desired sound broadcast wave rangeand to have a narrow pass range while in the other position the switchopen-circuits the tuning condenser and switches in a small condenser andshunt resistance combination I I, I2 which fixedly tunes the inputcircuit coil 6 to the predetermined frequency and gives it the desiredwide pass range. The output from this mixing valve M is coupled to afixed tuned further intermediate frequency amplifier as in the usualway. Each of the intermediate frequency tuned circuits of this amplifier(only the first stage of the said amplifier is illustrated, this stageincluding the valve 15) is shunted by-a resistance 16 when the switch sis in the position shown contacting switch contacts l1, l3, fortelevision receptionso that each resistance I6 broadens the pass rangeof its associated circuit sufiiciently for the television signals. Allthe other intermediate frequency stages (if any) are like thatillustrated and therefore it is not thought necessary to show suchfurther stages nor the rest of the receiver which is as well known perse, and includes thenecessary demodulating and translating apparatustogether with filters and/or change-over switches for enablingtelevision or sound reproduction to be effected. 7

It will be seen that in Figure 1 for short wave television reception,the variably tunable carrier stages of'the sound broadcast receivingapparatus are fixed tuned to a predetermined frequency, and act asintermediate frequency stages as respect the incoming short waves, whilethe pass band of the carrier stages of the said sound broadcastreceiving apparatus is widened to pass the television signals. For soundreception on broadcast waves the said sound broadcast receivingapparatus operates in the normal manner. Preferably all the switchesabove described are gang controlled, indicated schematically by the dashline 26, with a switch a which, in the sound reception position,switches in the broadcast receiving aerial [4 so that for televisionreception the operator has merely to throw the switch control into theposition appropriate to television reception and then effect tuningmerely by varying the control handle to which the tuning reactance ofthe first local oscillator 4 and that of short wave tuned circuit (orcir cuits) are ganged. Only one such short wave tuned circuit isactually shown, namely the circuit 2.

r 'In the embodiment of Figure 1 when television reception is to beeffected the variably tunable carrier stages of the sound receivingbroadcast apparatus are fixed tuned to a predetermined frequency byconnecting small shunt condensers (l I, ll) thereacross. The provisionof such shunt condensers is not, however, necessary and by suitabledesign the self-capacities of the inductances (G, 6) in the tunedcircuits in question may be caused fixedly to tune the said cir- .1

cuits to the desired predetermined frequency.

In the modification partly illustrated in Fig ures 2 and 3 wherein thevariably tunable carrier circuits of the sound broadcast receivingapparatus are converted into fixedly tuned intermediatefrequency'carrier circuits for television reception, the required fixedintermediate carrier frequency tuning is obtained without the need forproviding any switches afiecting the tuning of the stages in question,but merely by so arranging the tuning controls as to ensure that fortelevision reception the circuits in question are tuned by their normalcontrols to a predetermined frequency, preferably the lowest frequencyin their tuning range' For example in a receiver wherein the variablytunable carrier stages of the broadcast receiving apparatus are tunedeach by a variable condenser in a gang of condensers operable by acommon control knob the gang shaft which is operated by a knob t2carries a pointer I 9 moving over a scale 20 marked with the broadcasttuning range (for example 250 to 550 meters) and there-is provided anadditional mark 2| on the scale below the 250 meters markthis'additional mark being labelled Television. A convenient arrangementis shown in Figure 3 in which the tuning knob 22 drives the gang shaft23 through a friction clutch 24 and the said gang shaft has a televisionreception, the necessary resistances are switched into the carriercircuits of the sound broadcast receiving apparatus to broaden theacceptance band thereof to the extent necessary for televisionreception.

Although in the above described embodiments the use of shunt resistancesfor the purpose of broadening the acceptance band of the sound broadcastreceiving apparatus is referred to, obviously other expedients known perse, may be resorted to without departing from the spirit and scope ofthe appended claims.

Having now particularly described and ascertained the nature of myinvention and in what manner the same is to be performed I declare thatwhat I claim is:

1. A receiving system for the selective reception of sound signalstransmitted on a carrier within the broadcast band and of televisionsignals transmitted on a carrier within a widely separated frequencyband, comprising a vacuum tube amplifier having an input circuit tunableto desired frequencies Within the broadcast band and capable of passinga narrow range of modulation frequencies, said input circuit beingconstituted by an inductance and a variable condenser, and means forconverting said tunable input circuit to a fixedly tuned circuit whichis resonant to a frequency within said widely separated frequency bandfor television signals and which is capable of passing a range ofmodulation frequencies several times wider than the range of modulationfrequencies passed by the tunable circuit in the reception of soundsignals, said fixedly tuned circuit being constituted by said inductanceand a parallel combination of a resistance and a capacity connected inshunt to said inductance,

said converting means comprising switch means for selectively connectingin shunt to the in ductance the variable condenser or the parallelcombination of said resistance and capacity.

2. A receiving system for the selective reception of sound signalstransmitted on a carrier within the broadcast band and of televisionsignals transmitted on a carrierwithin awidely separated frequency band,comprising a vacuum tube amplifier having an inductance connected to theinput electrodes thereof, a variable condenser adapted to be connectedacross said inductance to form therewith a circuit tunable to desiredfrequencies within the broadcast band and capable of passing a narrowrange of modulation frequencies, a fixed condenser and a shuntresistance adapted to be connected across said inductance to formtherewith a fixedly tuned circuit which is resonant to a frequent withinsaid widely separated frequency band for television signals and which iscapable of passing a range of modulation frequencies several times widerthan the range of modulation frequencies passed by the tunable circuitin the reception of sound signals, and means for selectively connectingsaid variable condenser or said fixed condenser-resistance combinationacross said inductance.

3. A receiving system for the selective reception of signals transmittedin widely different channels of the frequency spectrum, such as forexample, a sound signal channel having a carrier in the broadcast handbetween 250 and 550 meters and requiring modulation frequencies of about10 kc. wide, and a television signal channel having a carrier belowabout 100 meters and requiring modulation frequencies several timeswider than those of the sound signal channel, comprising a conventionalsound broadcast receiver provided with at least one resonant circuitconstituted by an inductance and a shunt variable condenser which aretunable to a frequency within the broadcast band and are capable ofpassing only a limited band of modulation frequencies, a circuitresponsive to television signals in a channel below 100 meters coupledto said sound receiver, means adapted to cooperate with said inductanceof the sound receiver to resonate at a frequency in said short wavechannel and to pass the rela-

